Chapter 2: Image Quality Factors

A comprehensive set of vocabulary flashcards covering the primary exposure factors, image quality properties, and digital imaging technologies discussed in Chapter 2.

Exposure time ($T$)

A measure of how long the exposure will continue, measured in units of seconds, fractions of seconds, or milliseconds ($1\,millisecond = 0.001\,seconds$).

Milliamperage ($mA$)

A measure of the current flow rate in the x-ray tube circuit which indicates the number of x-ray photons produced per second.

$$mAs$$

The product of $mA$ and time in seconds ($mA \times \text{time (s)} = mAs$), which indicates the total quantity of radiation produced in the exposure.

Kilovoltage ($kVp$)

A measure of the potential difference across the x-ray tube that determines the speed and kinetic energy of electrons, influencing x-ray photon energy and penetration.

Source-image distance ($SID$)

The distance between the x-ray tube and the image receptor ($IR$), which inversely affects x-ray beam intensity and image exposure.

Object-image distance ($OID$)

The distance between the object or body part and the image receptor ($IR$).

Inverse Square Law

A law stating that radiation intensity is inversely proportional to the square of the $SID$, expressed as $\frac{I_{orig}}{I_{new}} = \frac{SID_{new}^2}{SID_{orig}^2}$.

$mAs$-distance formula

The formula used to compensate for changes in $SID$ to maintain image quality: $\frac{mAs_{orig}}{mAs_{new}} = \frac{SID_{orig}^2}{SID_{new}^2}$.

Technique Charts

Resources that provide recommended $kVp$, $mA$, and $mAs$ values for various exams and patient sizes.

Computed Radiography ($CR$)

A digital imaging system that uses an imaging plate with a photostimulable phosphor which must be processed in a separate reader.

Digital Radiography ($DR$)

A digital imaging system without cassettes that utilizes a fixed image receptor and displays images on a monitor almost immediately after exposure.

Exposure Index ($EI$) number

A numerical indicator used in digital imaging to determine if an image has been overexposed or underexposed.

Picture Archiving and Communication System ($PACS$)

The hardware and software technology used to catalog, store, and retrieve images from all digital imaging systems in a healthcare facility.

Optical Density ($OD$)

The overall blackness or lack of blackness of an image; in digital systems, underexposure results in a grainy image.

Image Contrast

The difference in the optical density of adjacent structures within the image, primarily controlled by $kVp$.

Image Detail

The sharpness or blurriness of an image, which is affected by $SID$, $OID$, and focal-spot size.

Size Distortion

Also known as magnification, this is affected by $SID$ and $OID$; increased $SID$ and decreased $OID$ results in less magnification.

Shape Distortion

A variation in the shape of the image in comparison to the actual object caused by an incorrectly positioned body part or an angled central ray.

Shuttering

A postprocessing capability that involves adding black panels to the outside areas of an image to block excess light.

Electronic Masking

A digital manipulation technique also referred to as cropping.